Myc confers androgen-independent prostate cancer cell growth

A long noncoding RNA connects c-Myc to tumor metabolism

Long noncoding RNAs (lncRNAs) have been implicated in a variety of physiological and pathological processes, including cancer. In prostate cancer, prostate cancer gene expression marker 1 (PCGEM1) is an androgen-induced prostate-specific lncRNA whose overexpression is highly associated with prostate tumors. PCGEM1's tumorigenic potential has been recently shown to be in part due to its ability to activate androgen receptor (AR). Here, we report a novel function of PCGEM1 that provides growth advantages for cancer cells by regulating tumor metabolism via c-Myc activation. PCGEM1 promotes glucose uptake for aerobic glycolysis, coupling with the pentose phosphate shunt to facilitate biosynthesis of nucleotide and lipid, and generates NADPH for redox homeostasis. We show that PCGEM1 regulates metabolism at a transcriptional level that affects multiple metabolic pathways, including glucose and glutamine metabolism, the pentose phosphate pathway, nucleotide and fatty acid biosynthesis, and the tricarboxylic acid cycle. The PCGEM1-mediated gene regulation takes place in part through AR activation, but predominantly through c-Myc activation, regardless of hormone or AR status. Significantly, PCGEM1 binds directly to target promoters, physically interacts with c-Myc, promotes chromatin recruitment of c-Myc, and enhances its transactivation activity. We also identified a c-Myc binding domain on PCGEM1 that contributes to the PCGEM1-dependent c-Myc activation and target induction. Together, our data uncover PCGEM1 as a key transcriptional regulator of central metabolic pathways in prostate cancer cells. By being a coactivator for both c-Myc and AR, PCGEM1 reprograms the androgen network and the central metabolism in a tumor-specific way, making it a promising target for therapeutic intervention.

Androgen receptor (AR) suppresses normal human prostate epithelial cell proliferation via AR/β-catenin/TCF-4 complex inhibition of c-MYC transcription

INTRODUCTION

Physiologic testosterone continuously stimulates prostate stromal cell secretion of paracrine growth factors (PGFs), which if unopposed would induce hyperplastic overgrowth of normal prostate epithelial cells (PrECs).

METHODS

Lentiviral shRNA stable knock down of c-MYC, β-catenin, or TCF-4 completely inhibits normal (i.e., non-transformed) human PrECs growth. c-MYC enhancer driven reporter expression and growth is inhibited by two chemically distinct molecules, which prevent β-catenin signaling either by blocking TCF-4 binding (i.e., toxoflavin) or by stimulating degradation (i.e., AVX939). Recombinant DKK1 protein at a dose, which inhibits activation of canonical Wnt signaling does not inhibit PrEC growth. Nuclear β-catenin translocation and PrEC growth is prevented by both lack of PGFs or Akt inhibitor-I. Growth inhibition induced by lack of PGFs, toxoflavin, or Akt inhibitor-I is overcome by constitutive c-MYC transcription.

RESULTS

In the presence of continuous PGF signaling, PrEC hyperplasia is prevented by androgen binding to AR suppressing c-MYC transcription, resulting in G0 arrest/terminal differentiation independent of Rb, p21, p27, FoxP3, or down regulation of growth factors receptors and instead involves androgen-induced formation of AR/β-catenin/TCF-4 complexes, which suppress c-MYC transcription. Such suppression does not occur when AR is mutated in its zinc-finger binding domain.

DISCUSSION

Proliferation of non-transformed human PrECs is dependent upon c-MYC transcription via formation/binding of β-catenin/TCF-4 complexes at both 5' and 3' c-MYC enhancers stimulated by Wnt-independent, PGF induced Akt signaling. In the presence of continuous PGF signaling, PrEC hyperplasia is prevented by androgen-induced formation of AR/β-catenin/TCF-4 complexes, which retains binding to 3' c-MYC enhancer, but now suppresses c-MYC transcription.

The role of mRNA splicing in prostate cancer

Alternative splicing (AS) is a crucial step in gene expression. It is subject to intricate regulation, and its deregulation in cancer can lead to a wide array of neoplastic phenotypes. A large body of evidence implicates splice isoforms in most if not all hallmarks of cancer, including growth, apoptosis, invasion and metastasis, angiogenesis, and metabolism. AS has important clinical implications since it can be manipulated therapeutically to treat cancer and represents a mechanism of resistance to therapy. In prostate cancer (PCa) AS also plays a prominent role and this review will summarize the current knowledge of alternatively spliced genes with important functional consequences. We will highlight accumulating evidence on AS of the components of the two critical pathways in PCa: androgen receptor (AR) and phosphoinositide 3-kinase (PI3K). These observations together with data on dysregulation of splice factors in PCa suggest that AR and PI3K pathways may be interconnected with previously unappreciated splicing regulatory networks. In addition, we will discuss several lines of evidence implicating splicing regulation in the development of the castration resistance.

HES6 drives a critical AR transcriptional programme to induce castration-resistant prostate cancer through activation of an E2F1-mediated cell cycle network

Castrate-resistant prostate cancer (CRPC) is poorly characterized and heterogeneous and while the androgen receptor (AR) is of singular importance, other factors such as c-Myc and the E2F family also play a role in later stage disease. HES6 is a transcription co-factor associated with stem cell characteristics in neural tissue. Here we show that HES6 is up-regulated in aggressive human prostate cancer and drives castration-resistant tumour growth in the absence of ligand binding by enhancing the transcriptional activity of the AR, which is preferentially directed to a regulatory network enriched for transcription factors such as E2F1. In the clinical setting, we have uncovered a HES6-associated signature that predicts poor outcome in prostate cancer, which can be pharmacologically targeted by inhibition of PLK1 with restoration of sensitivity to castration. We have therefore shown for the first time the critical role of HES6 in the development of CRPC and identified its potential in patient-specific therapeutic strategies.

The many faces of neuroendocrine differentiation in prostate cancer progression

In normal prostate, neuroendocrine (NE) cells are rare and interspersed among the epithelium. These cells are believed to provide trophic signals to epithelial cell populations through the secretion of an abundance of neuropeptides that can diffuse to influence surrounding cells. In the setting of prostate cancer (PC), NE cells can also stimulate surrounding prostate adenocarcinoma cell growth, but in some cases adenocarcinoma cells themselves acquire NE characteristics. This epithelial plasticity is associated with decreased androgen receptor (AR) signaling and the accumulation of neuronal and stem cell characteristics. Transformation to an NE phenotype is one proposed mechanism of resistance to contemporary AR-targeted treatments, is associated with poor prognosis, and thought to represent up to 25% of lethal PCs. Importantly, the advent of high-throughput technologies has started to provide clues for understanding the complex molecular profiles of tumors exhibiting NE differentiation. Here, we discuss these recent advances, the multifaceted manner by which an NE-like state may arise during the different stages of disease progression, and the potential benefit of this knowledge for the management of patients with advanced PC.

Cross modulation between the androgen receptor axis and protocadherin-PC in mediating neuroendocrine transdifferentiation and therapeutic resistance of prostate cancer

Castration-resistant prostate cancers (CRPCs) that relapse after androgen deprivation therapies (ADTs) are responsible for the majority of mortalities from prostate cancer (PCa). While mechanisms enabling recurrent activity of androgen receptor (AR) are certainly involved in the development of CRPC, there may be factors that contribute to the process including acquired neuroendocrine (NE) cell-like behaviors working through alternate (non-AR) cell signaling systems or AR-dependent mechanisms. In this study, we explore the potential relationship between the AR axis and a novel putative marker of NE differentiation, the human male protocadherin-PC (PCDH-PC), in vitro and in human situations. We found evidence for an NE transdifferentiation process and PCDH-PC expression as an early-onset adaptive mechanism following ADT and elucidate AR as a key regulator of PCDH-PC expression. PCDH-PC overexpression, in turn, attenuates the ligand-dependent activity of the AR, enabling certain prostate tumor clones to assume a more NE phenotype and promoting their survival under diverse stress conditions. Acquisition of an NE phenotype by PCa cells positively correlated with resistance to cytotoxic agents including docetaxel, a taxane chemotherapy approved for the treatment of patients with metastatic CRPC. Furthermore, knockdown of PCDH-PC in cells that have undergone an NE transdifferentiation partially sensitized cells to docetaxel. Together, these results reveal a reciprocal regulation between the AR axis and PCDH-PC signals, observed both in vitro and in vivo, with potential implications in coordinating NE transdifferentiation processes and progression of PCa toward hormonal and chemoresistance.

Prostate cancer originating in basal cells progresses to adenocarcinoma propagated by luminal-like cells

The relationship between the cells that initiate cancer and the cancer stem-like cells that propagate tumors has been poorly defined. In a human prostate tissue transformation model, basal cells expressing the oncogenes Myc and myristoylated AKT can initiate heterogeneous tumors. Tumors contain features of acinar-type adenocarcinoma with elevated eIF4E-driven protein translation and squamous cell carcinoma marked by activated beta-catenin. Lentiviral integration site analysis revealed that alternative histological phenotypes can be clonally derived from a common cell of origin. In advanced disease, adenocarcinoma can be propagated by self-renewing tumor cells with an androgen receptor-low immature luminal phenotype in the absence of basal-like cells. These data indicate that advanced prostate adenocarcinoma initiated in basal cells can be maintained by luminal-like tumor-propagating cells. Determining the cells that maintain human prostate adenocarcinoma and the signaling pathways characterizing these tumor-propagating cells is critical for developing effective therapeutic strategies against this population.

USP22 regulates oncogenic signaling pathways to drive lethal cancer progression

Increasing evidence links deregulation of the ubiquitin-specific proteases 22 (USP22) deubitiquitylase to cancer development and progression in a select group of tumor types, but its specificity and underlying mechanisms of action are not well defined. Here we show that USP22 is a critical promoter of lethal tumor phenotypes that acts by modulating nuclear receptor and oncogenic signaling. In multiple xenograft models of human cancer, modeling of tumor-associated USP22 deregulation demonstrated that USP22 controls androgen receptor accumulation and signaling, and that it enhances expression of critical target genes coregulated by androgen receptor and MYC. USP22 not only reprogrammed androgen receptor function, but was sufficient to induce the transition to therapeutic resistance. Notably, in vivo depletion experiments revealed that USP22 is critical to maintain phenotypes associated with end-stage disease. This was a significant finding given clinical evidence that USP22 is highly deregulated in tumors, which have achieved therapeutic resistance. Taken together, our findings define USP22 as a critical effector of tumor progression, which drives lethal phenotypes, rationalizing this enzyme as an appealing therapeutic target to treat advanced disease.

Systemic GLIPR1-ΔTM protein as a novel therapeutic approach for prostate cancer

GLIPR1 is a p53 target gene known to be downregulated in prostate cancer, and increased endogenous GLIPR1 expression has been associated with increased production of reactive oxygen species, increased apoptosis, decreased c-Myc protein levels and increased cell cycle arrest. Recently, we found that upregulation of GLIPR1 in prostate cancer cells increases mitotic catastrophe through interaction with heat shock cognate protein 70 (Hsc70) and downregulation of Aurora kinase A and TPX2. In this study, we evaluated the mechanisms of recombinant GLIPR1 protein (glioma pathogenesis-related protein 1-transmembrane domain deleted [GLIPR1-ΔTM]) uptake by prostate cancer cells and the efficacy of systemic GLIPR1-ΔTM administration in a prostate cancer xenograft mouse model. GLIPR1-ΔTM was selectively internalized by prostate cancer cells, leading to increased apoptosis through reactive oxygen species production and to decreased c-Myc protein levels. Interestingly, GLIPR1-ΔTM was internalized through clathrin-mediated endocytosis in association with Hsc70. Systemic administration of GLIPR1-ΔTM significantly inhibited VCaP xenograft growth. GLIPR1-ΔTM showed no evidence of toxicity following elimination from mouse models 8 hr after injection. Our results demonstrate that GLIPR1-ΔTM is selectively endocytosed by prostate cancer cells, leading to increased reactive oxygen species production and apoptosis, and that systemic GLIPR1-ΔTM significantly inhibits growth of VCaP xenografts without substantial toxicity.

Disruption of prostate epithelial differentiation pathways and prostate cancer development

One of the foremost problems in the prostate cancer (PCa) field is the inability to distinguish aggressive from indolent disease, which leads to difficult prognoses and thousands of unnecessary surgeries. This limitation stems from the fact that the mechanisms of tumorigenesis in the prostate are poorly understood. Some genetic alterations are commonly reported in prostate tumors, including upregulation of Myc, fusion of Ets genes to androgen-regulated promoters, and loss of Pten. However, the specific roles of these aberrations in tumor initiation and progression are poorly understood. Likewise, the cell of origin for PCa remains controversial and may be linked to the aggressive potential of the tumor. One important clue is that prostate tumors co-express basal and luminal protein markers that are restricted to their distinct cell types in normal tissue. Prostate epithelium contains layer-specific stem cells as well as rare bipotent cells, which can differentiate into basal or luminal cells. We hypothesize that the primary oncogenic cell of origin is a transient-differentiating bipotent cell. Such a cell must maintain tight temporal and spatial control of differentiation pathways, thus increasing its susceptibility for oncogenic disruption. In support of this hypothesis, many of the pathways known to be involved in prostate differentiation can be linked to genes commonly altered in PCa. In this article, we review what is known about important differentiation pathways (Myc, p38MAPK, Notch, PI3K/Pten) in the prostate and how their misregulation could lead to oncogenesis. Better understanding of normal differentiation will offer new insights into tumor initiation and may help explain the functional significance of common genetic alterations seen in PCa. Additionally, this understanding could lead to new methods for classifying prostate tumors based on their differentiation status and may aid in identifying more aggressive tumors.

Sensitivity and mechanisms of taxol-resistant prostate adenocarcinoma cells to Vernonia amygdalina extract

Prostate cancer (PC) patients once Paclitaxel (TAX) treatment responsive later develop hormone refractory PC, thus becoming TAX-insensitive. This underscores the urgent need to develop novel anti-PC therapies. Vernonia amygdalina (VA) could be one such candidate agent. We have shown that androgen-independent PC-3 cells are sensitive to VA treatment in vitro. VA extract (0.01, 0.1 and 1 mg/ml) inhibited DNA synthesis by 12%, 45% (p<0.05), and 73% (p<0.01) respectively. In contrast, TAX (0.01, 0.1, and 1 μM) failed to significantly affect cell growth, suggesting TAX resistance. We tested molecular mechanisms which may lend to the observed PC-3 cell VA sensitivity/TAX resistance. Though both VA and TAX stimulated MAPK activity, VA's induction was more intense, but transient, compared to TAX's sustained action. NF-κB activation was inhibited on average by 50% by either 1 mg/ml VA or 1 μM TAX. VA extract caused 35% and 45% increases in c-Myc activity at 10 and 60 min intervals respectively, with the highest stimulation attained 1h after treatment. In contrast, similar levels were attained by TAX rapidly (within 5 min) and were sustained compared to the slow/multi-phasic action of VA. VA extract treatments had no effect on AKT gene expression, while TAX treatments yielded a four-fold (P<0.01) increase; and P-glycoprotein (P-gp) activity was inhibited by VA and stimulated by TAX, compared to control (basal ATPase activity). This study shows that TAX-resistant PC-3 cells are sensitive to VA, perhaps explained by differential regulatory patterns of MAPK, c-Myc, AKT, and Pgp activities/expressions.

Prostate cancer progression after androgen deprivation therapy: mechanisms of castrate resistance and novel therapeutic approaches

Prostate cancer is the second-leading cause of cancer-related mortality in men in Western societies. Androgen receptor (AR) signaling is a critical survival pathway for prostate cancer cells, and androgen-deprivation therapy (ADT) remains the principal treatment for patients with locally advanced and metastatic disease. Although a majority of patients initially respond to ADT, most will eventually develop castrate resistance, defined as disease progression despite serum testosterone levels of <20 ng/dl. The recent discovery that AR signaling persists during systemic castration via intratumoral production of androgens led to the development of novel anti-androgen therapies including abiraterone acetate and enzalutamide. Although these agents effectively palliate symptoms and prolong life, metastatic castration-resistant prostate cancer remains incurable. An increased understanding of the mechanisms that underlie the pathogenesis of castrate resistance is therefore needed to develop novel therapeutic approaches for this disease. The aim of this review is to summarize the current literature on the biology and treatment of castrate-resistant prostate cancer.

Androgen receptor promotes ligand-independent prostate cancer progression through c-Myc upregulation

The androgen receptor (AR) is the principal therapeutic target in prostate cancer. For the past 70 years, androgen deprivation therapy (ADT) has been the major therapeutic focus. However, some patients do not benefit, and those tumors that do initially respond to ADT eventually progress. One recently described mechanism of such an effect is growth and survival-promoting effects of the AR that are exerted independently of the AR ligands, testosterone and dihydrotestosterone. However, specific ligand-independent AR target genes that account for this effect were not well characterized. We show here that c-Myc, which is a key mediator of ligand-independent prostate cancer growth, is a key ligand-independent AR target gene. Using microarray analysis, we found that c-Myc and AR expression levels strongly correlated with each other in tumors from patients with castration-resistant prostate cancer (CRPC) progressing despite ADT. We confirmed that AR directly regulates c-Myc transcription in a ligand-independent manner, that AR and c-Myc suppression reduces ligand-independent prostate cancer cell growth, and that ectopic expression of c-Myc attenuates the anti-growth effects of AR suppression. Importantly, treatment with the bromodomain inhibitor JQ1 suppressed c-Myc function and suppressed ligand-independent prostate cancer cell survival. Our results define a new link between two critical proteins in prostate cancer – AR and c-Myc – and demonstrate the potential of AR and c-Myc-directed therapies to improve prostate cancer control.

Advancing precision medicine for prostate cancer through genomics

Prostate cancer is the most common type of cancer in men and the second leading cause of cancer death in men in the United States. The recent surge of high-throughput sequencing of cancer genomes has supported an expanding molecular classification of prostate cancer. Translation of these basic science studies into clinically valuable biomarkers for diagnosis and prognosis and biomarkers that are predictive for therapy is critical to the development of precision medicine in prostate cancer. We review potential applications aimed at improving screening specificity in prostate cancer and differentiating aggressive versus indolent prostate cancers. Furthermore, we review predictive biomarker candidates involving ETS gene rearrangements, PTEN inactivation, and androgen receptor signaling. These and other putative biomarkers may signify aberrant oncogene pathway activation and provide a rationale for matching patients with molecularly targeted therapies in clinical trials. Lastly, we advocate innovations for clinical trial design to incorporate tumor biopsy and molecular characterization to develop biomarkers and understand mechanisms of resistance.

c-MYC-induced sebaceous gland differentiation is controlled by an androgen receptor/p53 axis

Although the sebaceous gland (SG) plays an important role in skin function, the mechanisms regulating SG differentiation and carcinoma formation are poorly understood. We previously reported that c-MYC overexpression stimulates SG differentiation. We now demonstrate roles for the androgen receptor (AR) and p53. MYC-induced SG differentiation was reduced in mice lacking a functional AR. High levels of MYC triggered a p53-dependent DNA damage response, leading to accumulation of proliferative SG progenitors and inhibition of AR signaling. Conversely, testosterone treatment or p53 deletion activated AR signaling and restored MYC-induced differentiation. Poorly differentiated human sebaceous carcinomas exhibited high p53 and low AR expression. Thus, the consequences of overactivating MYC in the SG depend on whether AR or p53 is activated, as they form a regulatory axis controlling proliferation and differentiation.

The enzymatic activity of apoptosis-inducing factor supports energy metabolism benefiting the growth and invasiveness of advanced prostate cancer cells

Apoptosis-inducing factor (AIF) promotes cell death yet also controls mitochondrial homeostasis and energy metabolism. It is unclear how these activities are coordinated, and the impact of AIF upon human disease, in particular cancer, is not well documented. In this study we have explored the contribution of AIF to the progression of prostate cancer. Analysis of archival gene expression data demonstrated that AIF transcript levels are elevated in human prostate cancer, and we found that AIF protein is increased in prostate tumors. Suppression of AIF expression in the prostate cancer cell lines LNCaP, DU145, and PC3 demonstrated that AIF does not contribute to cell toxicity via a variety of chemical death triggers, and growth under nutrient-rich conditions is largely unaffected by AIF ablation. However, under growth stress conditions, AIF depletion from DU145 and PC3 cell lines led to significant reductions in cell survival and growth that were not observed in LNCaP cells. Moreover AIF-deficient PC3 cells exhibited substantial reduction of tumorigenic growth in vivo. This reduced survival correlated with decreased expression of mitochondrial complex I protein subunits and concomitant changes in glucose metabolism. Finally, restoration of AIF-deficient PC3 cells with AIF variants demonstrated that the enzymatic activity of AIF is required for aggressive growth. Overall these studies show that AIF is an important factor for advanced prostate cancer cells and that through control of energy metabolism and redox balance, the enzymatic activity of AIF is critical for this support.

Epigenetics in prostate cancer

Prostate cancer (PC) is the most commonly diagnosed nonskin malignancy and the second most common cause of cancer death among men in the United States. Epigenetics is the study of heritable changes in gene expression caused by mechanisms other than changes in the underlying DNA sequences. Two common epigenetic mechanisms, DNA methylation and histone modification, have demonstrated critical roles in prostate cancer growth and metastasis. DNA hypermethylation of cytosine-guanine (CpG) rich sequence islands within gene promoter regions is widespread during neoplastic transformation of prostate cells, suggesting that treatment-induced restoration of a “normal” epigenome could be clinically beneficial. Histone modification leads to altered tumor gene function by changing chromosome structure and the level of gene transcription. The reversibility of epigenetic aberrations and restoration of tumor suppression gene function have made them attractive targets for prostate cancer treatment with modulators that demethylate DNA and inhibit histone deacetylases.

Androgen suppresses proliferation of castration-resistant LNCaP 104-R2 prostate cancer cells through androgen receptor, Skp2, and c-Myc

Androgen ablation therapy is the primary treatment for metastatic prostate cancer. However, this therapy is associated with several undesired side-effects, including increased risk of cardiovascular diseases. To study if termination of long-term androgen ablation and restoration of testosterone levels could suppress the growth of relapsed hormone-refractory prostate tumors, we implanted testosterone pellets in castrated nude mice carrying androgen receptor (AR)-positive LNCaP 104-R2 cells, which relapsed from androgen-dependent LNCaP 104-S cells after long-term androgen deprivation. 104-R2 tumor xenografts regressed after testosterone pellets were implanted. Of 33 tumors, 24 adapted to elevation of testosterone level and relapsed as androgen-insensitive tumors. Relapsed tumors (R2Ad) expressed less AR and prostate-specific antigen. We then studied the molecular mechanism underlying the androgenic regulation of prostate cancer cell proliferation. Androgen suppresses proliferation of 104-R2 by inducing G(1) cell cycle arrest through reduction of S-phase kinase-associated protein 2 (Skp2) and c-Myc, and induction of p27(Kip1). 104-R2 cells adapted to androgen treatment and the adapted cells, R2Ad, were androgen-insensitive cells with a slower growth rate and low protein level of AR, high levels of c-Myc and Skp2, and low levels of p27(Kip1). Nuclear AR and prostate-specific antigen expression is present in 104-R2 cells but not R2Ad cells when androgen is absent. Overexpression of AR in R2Ad cells regenerated an androgen-repressed phenotype; knockdown of AR in 104-R2 cells generated an androgen-insensitive phenotype. Overexpression of Skp2 and c-Myc in 104-R2 cells blocked the growth inhibition caused by androgens. We concluded that androgens cause growth inhibition in LNCaP 104-R2 prostate cancer cells through AR, Skp2, and c-Myc.

Troglitazone suppresses c-Myc levels in human prostate cancer cells via a PPARγ-independent mechanism

Troglitazone is a ligand for the peroxisome proliferator activated receptor gamma (PPARγ) that decreases growth of human prostate cancer cells in vitro and in vivo. However, the mechanism by which troglitazone reduces prostate cancer cell growth is not fully understood. To understand the signaling pathways involved in troglitazone-induced decreases in prostate cancer growth, we examined the effect of troglitazone on androgen-independent C4-2 human prostate cancer cells. Initial experiments revealed troglitazone inhibited C4-2 cell proliferation by arresting cells in the G(0)/G(1) phase of the cell cycle and inducing apoptosis. Since the proto-oncogene product c-Myc regulates both apoptosis and cell cycle progression, we next examined whether troglitazone altered expression of c-Myc. Troglitazone decreased c-Myc protein levels as well as expression of downstream targets of c-Myc in a dose-dependent manner. In C4-2 cells, troglitazone-induced decreases in c-Myc protein involve proteasome-mediated degradation of c-Myc protein as well as reductions in c-Myc mRNA levels. It appears that troglitazone stimulates degradation of c-Myc by increasing c-Myc phosphorylation, for the level of phosphorylated c-Myc was elevated in prostate cancer cells exposed to troglitazone. While troglitazone dramatically decreased the amount of c-Myc within C4-2 cells, the PPARγ ligands ciglitazone, rosiglitazone and pioglitazone did not reduce c-Myc protein levels. Furthermore the down-regulation of c-Myc by troglitazone was not blocked by the PPARγ antagonist GW9662 and siRNA-mediated decreases in PPARγ protein. Thus, our data suggest that troglitazone reduces c-Myc protein independently of PPARγ.

SKP2 oncogene is a direct MYC target gene and MYC down-regulates p27(KIP1) through SKP2 in human leukemia cells

SKP2 is the ubiquitin ligase subunit that targets p27(KIP1) (p27) for degradation. SKP2 is induced in the G(1)-S transit of the cell cycle, is frequently overexpressed in human cancer, and displays transformation activity in experimental models. Here we show that MYC induces SKP2 expression at the mRNA and protein levels in human myeloid leukemia K562 cells with conditional MYC expression. Importantly, in these systems, induction of MYC did not activate cell proliferation, ruling out SKP2 up-regulation as a consequence of cell cycle entry. MYC-dependent SKP2 expression was also detected in other cell types such as lymphoid, fibroblastic, and epithelial cell lines. MYC induced SKP2 mRNA expression in the absence of protein synthesis and activated the SKP2 promoter in luciferase reporter assays. With chromatin immunoprecipitation assays, MYC was detected bound to a region of human SKP2 gene promoter that includes E-boxes. The K562 cell line derives from human chronic myeloid leukemia. In a cohort of chronic myeloid leukemia bone marrow samples, we found a correlation between MYC and SKP2 mRNA levels. Analysis of cancer expression databases also indicated a correlation between MYC and SKP2 expression in lymphoma. Finally, MYC-induced SKP2 expression resulted in a decrease in p27 protein in K562 cells. Moreover, silencing of SKP2 abrogated the MYC-mediated down-regulation of p27. Our data show that SKP2 is a direct MYC target gene and that MYC-mediated SKP2 induction leads to reduced p27 levels. The results suggest the induction of SKP2 oncogene as a new mechanism for MYC-dependent transformation.

Effect of artemisinin derivatives on apoptosis and cell cycle in prostate cancer cells

Artemisinin is a plant-derived anti-malarial drug that has relatively low toxicity in humans and is activated by heme and/or intracellular iron leading to intracellular free radical formation. Interestingly, artemisinin has displayed anti-cancer activity, with artemisinin dimers being more potent than monomeric artemisinin. Intracellular iron uptake is regulated by the transferrin receptor (TfR), and the activity of artemisinin depends on the availability of iron. We examined the level of TfR in prostate cancer (PCa) tumor cells, synthesized two new artemisinin dimers, and evaluated the effect of dihydroartemisinin and artemisinin dimers, ON-2Py and 2Py, on proliferation and apoptosis in PCa cells. TfR was expressed in the majority of PCa bone and soft tissue metastases, all 24 LuCaP PCa xenografts, and PCa cell lines. After treatment with dihydroartemisinin, ON-2Py, or 2Py all PCa cell lines displayed dose-dependent decrease in cell number. 2Py was most effective in decreasing cell number. An increase in apoptotic events and growth arrest was observed in the C4-2 and LNCaP cell lines. Growth arrest was observed in PC-3 cells, but no significant change was observed in DU 145 cells. Treatment with 2Py resulted in a loss of the anti-apoptotic protein survivin in all four cell lines. 2Py treatment also decreased androgen receptor and prostate-specific antigen expression in C4-2 and LNCaP cells, with a concomitant loss of cell cycle regulatory proteins cyclin D1 and c-Myc. This study shows the potential use of artemisinin derivatives as therapeutic candidates for PCa and warrants the initiation of preclinical studies.

Regulation of ploidy and senescence by the AMPK-related kinase NUAK1

Senescence is an irreversible cell-cycle arrest that is elicited by a wide range of factors, including replicative exhaustion. Emerging evidences suggest that cellular senescence contributes to ageing and acts as a tumour suppressor mechanism. To identify novel genes regulating senescence, we performed a loss-of-function screen on normal human diploid fibroblasts. We show that downregulation of the AMPK-related protein kinase 5 (ARK5 or NUAK1) results in extension of the cellular replicative lifespan. Interestingly, the levels of NUAK1 are upregulated during senescence whereas its ectopic expression triggers a premature senescence. Cells that constitutively express NUAK1 suffer gross aneuploidies and show diminished expression of the genomic stability regulator LATS1, whereas depletion of NUAK1 with shRNA exerts opposite effects. Interestingly, a dominant-negative form of LATS1 phenocopies NUAK1 effects. Moreover, we show that NUAK1 phosphorylates LATS1 at S464 and this has a role in controlling its stability. In summary, our work highlights a novel role for NUAK1 in the control of cellular senescence and cellular ploidy.

Overexpression of the potential kinase serine/ threonine/tyrosine kinase 1 (STYK 1) in castration-resistant prostate cancer

Despite high response rates and clinical benefits, androgen ablation often fails to cure advanced or relapsed prostate cancer because castration-resistant prostate cancer (CRPC) cells inevitably emerge. CRPC cells not only grow under castration, but also behave more aggressively, indicating that a number of malignant signaling pathways are activated in CRPC cells as well as androgen receptor signaling. Based on information from the gene expression profiles of clinical CRPC cells, we here identified one overexpressed gene, serine/threonine/tyrosine kinase 1 (STYK1), encoding a potential kinase, as a molecular target for CRPC. RNA and immunohistochemical analyses validated the overexpression of STYK1 in prostate cancer cells, and its expression was distinct in CRPC cells. Knockdown of STYK1 by siRNA resulted in drastic suppression of prostate cancer cell growth and, concordantly, enforced expression of STYK1 promoted cell proliferation, whereas ectopic expression of a kinase-dead mutant STYK1 did not. An in vitro kinase assay using recombinant STYK1 demonstrated that STYK1 could have some potential as a kinase, although its specific substrates are unknown. These findings suggest that STYK1 could be a possible molecular target for CRPC, and small molecules specifically inhibiting STYK1 kinase could be a possible approach for the development of novel CRPC therapies.

Oncogenic activation of androgen receptor

BACKGROUND

There is considerable evidence implicating the aberrant activation or "reactivation" of androgen receptor in the course of androgen-ablation therapy as a potential cause for the development of castration-resistant prostate cancer. Several non-mutually exclusive mechanisms including the inappropriate activation of androgen receptor (AR) by non-steroids have been postulated. The present work is aimed to understand the role of neuropeptides released by neuroendocrine transdifferentiated prostate cancer cells in the aberrant activation of AR.

OBJECTIVES

The study was designed to study how neuropeptides such as gastrin-releasing peptide activate AR and to define the crucial signal pathways involved, in the hope to identify therapeutic targets.

METHODS AND MATERIALS

Androgen-dependent LNCaP cell line was used to study the effects of bombesin/gastrin-releasing peptide on the growth of the cell line and the transactivation of AR. The neuropeptide was either added to the media or introduced as a transgene in LNCaP cells to study its paracrine or autocrine effect on LNCaP growth under androgen-deprived conditions. The activation of AR was monitored by reporter assay, chromatin immunoprecipitation (ChIP) of AR, translocation into the nucleus and cDNA microarray of the AR response genes.

RESULTS

Bombesin/gastrin releasing peptides induce androgen-independent growth of LNCaP in vitro and in vivo. It does so by activating AR, which is accompanied by the activation of Src tyrosine kinase and its target c-myc oncogene. The bombesin or Src-activated AR induces an overlapping set of AR response genes as androgen, but they also a unique set of genes. Intriguingly, the Src-activated and androgen-bound ARs differ in their binding specificity toward AR response elements, indicating the receptors activated by these 2 mechanisms are not conformationally identical. Finally, Src inhibitor was shown to effectively block the activation of AR and the growth effects induced by bombesin.

CONCLUSION

The results showed that AR can be activated by neuropeptide, a ligand for G-protein coupled receptor, in the absence of androgen. The activation goes through Src-tyrosine kinase pathway, and tyrosine kinase inhibitor is a potentially useful adjunctive therapy during androgen ablation.

Activation of beta-Catenin in mouse prostate causes HGPIN and continuous prostate growth after castration

BACKGROUND

The role of Wnt/beta-Catenin signaling in embryogenesis and carcinogenesis has been extensively studied in organs such as colon, lung and pancreas, but little is known about Wnt/beta-Catenin signaling in the prostate. Although stabilizing mutations in APC and beta-Catenin are rare in primary prostate tumors, recent studies suggest that cytoplasmic/nuclear beta-Catenin is associated with advanced, metastatic, hormone-refractory prostate carcinoma.

METHODS

To better understand the role of beta-Catenin in prostatic development and carcinogenesis, we studied Wnt expression during prostate development and activated Wnt/beta-Catenin signaling in the developing and adult prostate.

RESULTS

Our results demonstrated that during prostate development Wnt ligands display a dynamic expression pattern. Activation of beta-Catenin during prostate development caused epithelial hyperplasia followed by prostatic intraepithelial neoplasia (PIN) in prostate. In the adult prostate, activation of beta-Catenin resulted in high grade PIN (HGPIN) and continuous prostatic growth after castration. As a result of activation of beta-Catenin, AR was first up-regulated with the emergence of epithelial hyperplasia, but was later down-regulated when HGPIN developed. Furthermore, activation of beta-Catenin induced Foxa2 re-expression in adult prostate which normally is only expressed in the embryonic budding stage during prostate development.

CONCLUSIONS

The results from this study strongly suggest that Wnt/beta-Catenin signaling is involved in the regulation of prostate development and confirm that constitutive activation of this pathway enables the mouse prostate to grow after castration.

Overexpression of CD24, c-myc and phospholipase 2A in prostate cancer tissue samples obtained by needle biopsy

Altered CD24, c-myc and phospholipase 2a expression was reported in different cancers. Our aim was to measure the expression of these genes in prostate cancer tissues, and compare it to non-cancerous samples. Prostate tissue samples were collected by needle biopsy from 20 prostate cancer (PCA) and 11 benign prostate hyperplasic (BPH) patients. RNA was isolated; cDNA synthetized, CD24, c-myc and phospholipase 2A (PL2A) expressions were determined by quantitative real-time PCR method. The expression of beta-globin gene was measured for normalization of the gene expression results. Serum prostate specific antigen (PSA) levels were determined by microparticle enzyme immunoassay (MEIA) method. PSA levels were significantly different between the PCA and BPH groups, 252.37 +/- 308.33 ng/ml vs. 3.5 +/- 2.14 ng/ml (p = 0.001), respectively. CD24 expression was 988.86 +/- 3041 ng/microl in prostate tumor and 4.00 +/- 4.25 ng/microl in the BPH group (p = 0.035). The c-myc expression was 88.32 +/- 11.93 ng/microl in the prostate tumor and 17.08 +/- 21.75 ng/microl in the BPH group (p = 0.02), and the PL2A 31.36 +/- 67.02 ng/microl was in PCA and 5.56 +/- 14.08 ng/microl in BPH (p = 0.025). Gleason's scores showed correlation with c-myc (p = 0.019) and PSA (p = 0.033) levels. Overexpression of PL2A, CD24 and c-myc was observed in prostate cancer samples using quantitative real-time PCR method.

An AR-Skp2 pathway for proliferation of androgen-dependent prostate-cancer cells

Androgen-androgen-receptor (androgen-AR) signaling in normal prostate epithelium promotes terminal luminal epithelial cell differentiation. In androgen-dependent prostate-cancer cells, androgen-AR signaling gains the ability to promote both differentiation and proliferation. How this signaling promotes proliferation of androgen-dependent prostate-cancer cells and its relationship with the differentiation-promoting functions of the AR are important issues regarding the biology of androgen-dependent prostate-cancer cells. Herein, we report the identification of an AR-Skp2 pathway in prostate-cancer cells that depend on the AR for proliferation; in this pathway, AR is a robust upstream regulator of Skp2 through blocking the D-box-dependent degradation of this protein, and Skp2, in turn, serves as an essential downstream effector of AR in promoting proliferation independently of the differentiation-promoting function of AR. These results provide new knowledge on how AR functions in androgen-dependent prostate-cancer cells and identify strategies to specifically target the proliferation-promoting function of AR without compromising cancer-cell differentiation.

Efficacy, pharmacokinetics, tisssue distribution, and metabolism of the Myc-Max disruptor, 10058-F4 [Z,E]-5-[4-ethylbenzylidine]-2-thioxothiazolidin-4-one, in mice

OBJECTIVES

c-Myc is commonly activated in many human tumors and is functionally important in cellular proliferation, differentiation, apoptosis and cell cycle progression. The activity of c-Myc requires noncovalent interaction with its client protein Max. In vitro studies indicate the thioxothiazolidinone, 10058-F4, inhibits c-Myc/Max dimerization. In this study, we report the efficacy, pharmacokinetics and metabolism of this novel protein-protein disruptor in mice.

METHODS

SCID mice bearing DU145 or PC-3 human prostate cancer xenografts were treated with either 20 or 30 mg/kg 10058-F4 on a qdx5 schedule for 2 weeks for efficacy studies. For pharmacokinetics and metabolism studies, mice bearing PC-3 or DU145 xenografts were treated with 20 mg/kg of 10058-F4 i.v. Plasma and tissues were collected 5-1440 min after dosing. The concentration of 10058-F4 in plasma and tissues was determined by HPLC, and metabolites were characterized by LC-MS/MS.

RESULTS

Following a single iv dose, peak plasma 10058-F4 concentrations of approximately 300 muM were seen at 5 min and declined to below the detection limit at 360 min. Plasma concentration versus time data were best approximated by a two-compartment, open, linear model. The highest tissue concentrations of 10058-F4 were found in fat, lung, liver, and kidney. Peak tumor concentrations of 10058-F4 were at least tenfold lower than peak plasma concentrations. Eight metabolites of 10058-F4 were identified in plasma, liver, and kidney. The terminal half-life of 10058-F4 was approximately 1 h, and the volume of distribution was >200 ml/kg. No significant inhibition of tumor growth was seen after i.v. treatment of mice with either 20 or 30 mg/kg 10058-F4.

CONCLUSION

The lack of significant antitumor activity of 10058-F4 in tumor-bearing mice may have resulted from its rapid metabolism and low concentration in tumors.

Genetic and genomic analysis modeling of germline c-MYC overexpression and cancer susceptibility

BACKGROUND

Germline genetic variation is associated with the differential expression of many human genes. The phenotypic effects of this type of variation may be important when considering susceptibility to common genetic diseases. Three regions at 8q24 have recently been identified to independently confer risk of prostate cancer. Variation at 8q24 has also recently been associated with risk of breast and colorectal cancer. However, none of the risk variants map at or relatively close to known genes, with c-MYC mapping a few hundred kilobases distally.

RESULTS

This study identifies cis-regulators of germline c-MYC expression in immortalized lymphocytes of HapMap individuals. Quantitative analysis of c-MYC expression in normal prostate tissues suggests an association between overexpression and variants in Region 1 of prostate cancer risk. Somatic c-MYC overexpression correlates with prostate cancer progression and more aggressive tumor forms, which was also a pathological variable associated with Region 1. Expression profiling analysis and modeling of transcriptional regulatory networks predicts a functional association between MYC and the prostate tumor suppressor KLF6. Analysis of MYC/Myc-driven cell transformation and tumorigenesis substantiates a model in which MYC overexpression promotes transformation by down-regulating KLF6. In this model, a feedback loop through E-cadherin down-regulation causes further transactivation of c-MYC.

CONCLUSION

This study proposes that variation at putative 8q24 cis-regulator(s) of transcription can significantly alter germline c-MYC expression levels and, thus, contribute to prostate cancer susceptibility by down-regulating the prostate tumor suppressor KLF6 gene.

Epigenetics of prostate cancer: beyond DNA methylation

Epigenetic mechanisms permit the stable inheritance of cellular properties without changes in DNA sequence or amount. In prostate carcinoma, epigenetic mechanisms are essential for development and progression, complementing, amplifying and diversifying genetic alterations. DNA hypermethylation affects at least 30 individual genes, while repetitive sequences including retrotransposons and selected genes become hypomethylated. Hypermethylation of several genes occurs in a coordinate manner early in carcinogenesis and can be exploited for cancer detection, whereas hypomethylation and further hypermethylation events are associated with progression. DNA methylation alterations interact with changes in chromatin proteins. Prominent alterations at this level include altered patterns of histone modification, increased expression of the EZH2 polycomb histone methyltransferase, and changes in transcriptional corepressors and coactivators. These changes may make prostate carcinoma particularly susceptible to drugs targeting chromatin and DNA modifications. They relate to crucial alterations in a network of transcription factors comprising ETS family proteins, the androgen receptor, NKX3.1, KLF, and HOXB13 homeobox proteins. This network controls differentiation and proliferation of prostate epithelial cells integrating signals from hormones, growth factors and cell adhesion proteins that are likewise distorted in prostate cancer. As a consequence, prostate carcinoma cells appear to be locked into an aberrant state, characterized by continued proliferation of largely differentiated cells. Accordingly, stem cell characteristics of prostate cancer cells appear to be secondarily acquired. The aberrant differentiation state of prostate carcinoma cells also results in distorted mutual interactions between epithelial and stromal cells in the tumor that promote tumor growth, invasion, and metastasis.

The use of whole genome amplification to study chromosomal changes in prostate cancer: insights into genome-wide signature of preneoplasia associated with cancer progression

Background

Prostate cancer (CaP) is a disease with multifactorial etiology that includes both genetic and environmental components. The knowledge of the genetic basis of CaP has increased over the past years, mainly in the pathways that underlie tumourigenesis, progression and drug resistance. The vast majority of cases of CaP are adenocarcinomas that likely develop through a pre-malignant lesion and high-grade prostatic intraepithelial neoplasia (HPIN). Histologically, CaP is a heterogeneous disease consisting of multiple, discrete foci of invasive carcinoma and HPIN that are commonly interspersed with benign glands and stroma. This admixture with benign tissue can complicate genomic analyses in CaP. Specifically, when DNA is bulk-extracted the genetic information obtained represents an average for all of the cells within the sample.

Results

To minimize this problem, we obtained DNA from individual foci of HPIN and CaP by laser capture microdissection (LCM). The small quantities of DNA thus obtained were then amplified by means of multiple-displacement amplification (MDA), for use in genomic DNA array comparative genomic hybridisation (gaCGH). Recurrent chromosome copy number abnormalities (CNAs) were observed in both HPIN and CaP. In HPIN, chromosomal imbalances involving chromosome 8 where common, whilst in CaP additional chromosomal changes involving chromosomes 6, 10, 13 and 16 where also frequently observed.

Conclusion

An overall increase in chromosomal changes was seen in CaP compared to HPIN, suggesting a universal breakdown in chromosomal stability. The accumulation of CNAs, which occurs during this process is non-random and may indicate chromosomal regions important in tumourigenesis. It is therefore likely that the alterations in copy number are part of a programmed cycle of events that promote tumour development, progression and survival. The combination of LCM, MDA and gaCGH is ideally suited for the identification of CNAs from small cell clusters and may assist in the discovery of potential genomic markers for early diagnosis, or identify the location of tumour suppressor genes (TSG) or oncogenes previously unreported in HPIN and CaP.

Growth inhibition and apoptosis induced by daunomycin-conjugated triplex-forming oligonucleotides targeting the c-myc gene in prostate cancer cells

Covalent attachment of intercalating agents to triplex-forming oligonucleotides (TFOs) is a promising strategy to enhance triplex stability and biological activity. We have explored the possibility to use the anticancer drug daunomycin as triplex stabilizing agent. Daunomycin-conjugated TFOs (dauno-TFOs) bind with high affinity and maintain the sequence-specificity required for targeting individual genes in the human genome. Here, we examined the effects of two dauno-TFOs targeting the c-myc gene on gene expression, cell proliferation and survival. The dauno-TFOs were directed to sequences immediately upstream (dauno-GT11A) and downstream (dauno-GT11B) the major transcriptional start site in the c-myc gene. Both dauno-TFOs were able to down-regulate promoter activity and transcription of the endogenous gene. Myc-targeted dauno-TFOs inhibited growth and induced apoptosis of prostate cancer cells constitutively expressing the gene. Daunomycin-conjugated control oligonucleotides with similar sequences had only minimal effects, confirming that the activity of dauno-TFOs was sequence-specific and triplex-mediated. To test the selectivity of dauno-TFOs, we examined their effects on growth of normal human fibroblasts, which express low levels of c-myc. Despite their ability to inhibit c-myc transcription, both dauno-TFOs failed to inhibit growth of normal fibroblasts at concentrations that inhibited growth of prostate cancer cells. In contrast, daunomycin inhibited equally fibroblasts and prostate cancer cells. Thus, daunomycin per se did not contribute to the antiproliferative activity of dauno-TFOs, although it greatly enhanced their ability to form stable triplexes at the target sites and down-regulate c-myc. Our data indicate that dauno-TFOs are attractive gene-targeting agents for development of new cancer therapeutics.

Stable expression of constitutively-activated STAT3 in benign prostatic epithelial cells changes their phenotype to that resembling malignant cells

Background

Signal transducers and activators of transcription (STATs) are involved in growth regulation of cells. They are usually activated by phosphorylation at specific tyrosine residues. In neoplastic cells, constitutive activation of STATs accompanies growth dysregulation and resistance to apoptosis through changes in gene expression, such as enhanced anti-apoptotic gene expression or reduced pro-apoptotic gene expression. Activated STAT3 is thought to play an important role in prostate cancer (PCA) progression. Because we are interested in how persistently-activated STAT3 changes the cellular phenotype to a malignant one in prostate cancer, we used expression vectors containing a gene for constitutively-activated STAT3, called S3c, into NRP-152 rat and BPH-1 human benign prostatic epithelial cells.

Results

We observed that prostatic cell lines stably expressing S3c required STAT3 expression for survival, because they became sensitive to antisense oligonucleotide for STAT3. However, S3c-transfected cells were not sensitive to the effects of JAK inhibitors, meaning that STAT3 was constitutively-activated in these transfected cell lines. NRP-152 prostatic epithelial cells lost the requirement for exogenous growth factors. Furthermore, we observed that NRP-152 expressing S3c had enhanced mRNA levels of retinoic acid receptor (RAR)-α, reduced mRNA levels of RAR-β and -γ, while BPH-1 cells transfected with S3c became insensitive to the effects of androgen, and also to the effects of a testosterone antagonist. Both S3c-transfected cell lines grew in soft agar after stable transfection with S3c, however neither S3c-transfected cell line was tumorigenic in severe-combined immunodeficient mice.

Conclusions

We conclude, based on our findings, that persistently-activated STAT3 is an important molecular marker of prostate cancer, which develops in formerly benign prostate cells and changes their phenotype to one more closely resembling transformed prostate cells. That the S3c-transfected cell lines require the continued expression of S3c demonstrates that a significant phenotypic change occurred in the cells. These conclusions are based on our data with respect to loss of growth factor requirement, loss of androgen response, gain of growth in soft agar, and changes in RAR subunit expression, all of which are consistent with a malignant phenotype in prostate cancer. However, an additional genetic change may be required for S3c-transfected prostate cells to become tumorigenic.

Triplex DNA-mediated downregulation of Ets2 expression results in growth inhibition and apoptosis in human prostate cancer cells

Ets2 is a member of the Ets family of transcription factors that in humans comprise 25 distinct members. Various Ets-domain transcription factors have been implicated in cancer development. Ets2 is expressed in prostate and breast cancer cells and is thought to have a role in promoting growth and survival in these cell types. However, a definitive role and the mechanisms whereby Ets2 acts in cancer cells are still unclear. Structural and functional similarities as well as overlapping DNA binding specificities complicate the identification of the specific roles of the various Ets factors. In this study, we used a triplex-forming oligonucleotide (TFO) to selectively inhibit Ets2 transcription in prostate cancer cells. We had previously shown that the Ets2-targeting TFO, which was directed to a unique purine-rich sequence critical for Ets2 promoter activity, acted with a high degree of sequence-specificity and target selectivity. TFO-mediated downregulation of Ets2 in prostate cancer cells induced important phenotypic changes, including inhibition of anchorage-dependent and anchorage -independent growth, cell cycle alterations and induction of apoptotic cell death. Expression of Ets2 under the control of a heterologous promoter abolished the anti-proliferative effects of the TFO in both short- and long-term assays, suggesting that these effects were a direct result of downregulation of Ets2 transcription and confirming target selectivity of the TFO. Furthermore, normal human fibroblasts, which expressed low levels of Ets2, were not affected by the Ets2-targeting TFO. Downregulation of Ets2 in prostate cancer cells was associated with reduced levels of the anti-apoptotic protein bcl-x(L) and growth regulatory factors cyclin D1 and c-myc. These data revealed a specific role of this transcription factor in promoting growth and survival of prostate cancer cells. Furthermore, the activity and selectivity of the Ets2-targeting TFO suggest that it might represent a valid approach to prostate cancer therapy.